import math
if __name__=="__main__":
    while True:
        n=int(input().strip())
        if n==0:
            break
        if n<=2:
            s=(n-1)*5+1.75
        else:
            s=2*5+(n-3)*3+1.75
        t=math.sqrt(2*s/9.8)
        print(round(t,3))
